Miss Blake, who suffers from a serious, life-threatening condition, was last seen on Sunday December 13 around Waltham Forest, east London, and police in Bexley, south-east London, believe she is still in the area.

Detectives say it is not known if the family are together.

Her partner, Arthur Simpson-Kent is also missing (Picture: PA)

Miss Blake’s silver-beige Renault Scenic was found in Calvert Avenue in Bethnal Green, east London, on January 3, but it is not known who parked it there.

Scotland Yard said the investigation continues to be a high-risk missing persons inquiry, but due to concerns for their welfare, the Homicide and Major Crime Command (HMCC) is now leading and is looking into whether the family may have been victims of a crime.

Detective Chief Inspector Graeme Gwyn of the HMCC, said: ‘A number of inquiries are under way to find Sian Blake, Arthur Simpson-Kent and their two children.

‘They have all been missing for a considerable period of time now, and I am growing increasingly concerned for their welfare.

‘In particular Sian suffers from a serious, life-threatening condition and we do not know if she is receiving the medication and treatment she requires to keep well.’

Ms Blake is black, 5ft 2in tall and slim with short black hair. She wears glasses but can also wear contact lenses.

Mr Simpson-Kent is a light-skinned black man who is 6ft 2in tall.

Anyone with information is asked to call police on 020 8721 4805 or Crimestoppers anonymously on 0800 555111.